Power amplifiers are used e.g. in radio base stations in mobile communication networks. The input signal for the power amplifiers is often biased to achieve a desired operating voltage for the input signal. This biasing can e.g. be performed in a driver circuit for a power amplifier. The source for the biasing can be provided by a DC (Direct Current) source.
JP2009044281 presents a FET amplifier circuit in which an FET amplifier element has improved switching speed. The FET amplifier circuit is provided with: a bias voltage sudden step-up circuit and a bias voltage sudden drop circuit. However, the presented amplifier circuit, while providing a bias, is unable to decouple the baseband from the biasing.
Another solution is to provide one or more capacitors as part of the biasing circuit to remove any RF components on the DC source and/or to provide a voltage stiff DC source for the biasing. A large capacitor is desired for a stable voltage level, but a small capacitor is desired to be able to switch off (and on) the biasing quickly, e.g. for Time-division Duplex operation such as for LTE (Long Term Evolution).
The balance between a large and a small capacitor is difficult to optimise and it would be ideal if the benefits of both small and large capacitors can somehow be achieved.